nmap
NetworkPackage: nmap
Scans a machine's ports from outside and shows what an attacker would see. Run it on your own servers after every firewall change — and only on your own.
What its options do in the lessons
From the same glossary the lessons render under their commands, so the two cannot disagree.
nmap -Pn- Skips host discovery and scans straight away. A server that blocks ping is declared "down" without this option, and no port gets tested — the first reflex for scanning a machine behind a firewall.
nmap -p-- Scans all 65,535 ports instead of the default thousand common ones. Slower, but the only scan that reveals a service on an unusual port — a debug tool, a port a dependency added.
nmap --reason- Shows the exact response behind each verdict (
syn-ack,no-response,reset), not just the state. Useful when a port is classified other than expected.